1. Field of the Invention
The present invention relates to the fields of diagnostic and therapeutic ultrasound, and more particularly, to novel methods and apparatus for performing diagnostic ultrasound simultaneously with the application of therapeutic ultrasonic waves to a region of a patient.
2. Background of the Invention
Diagnostic ultrasound refers to the imaging of a region of a human or animal patient using an ultrasound transducer to generate and receive ultrasonic waves. Typically, the transducer is placed on the patient's body over a region to be imaged and ultrasonic waves generated by the transducer are then directed at the region. The transducer then receives reflected ultrasonic waves from the region and converts the received waves into electrical signals from which an image is generated. Generally, better images are obtained with diagnostic ultrasound when higher frequency, lower energy ultrasonic waves are employed. Contrast agents can also be used to improve the quality of images obtained via diagnostic ultrasound. Exemplary contrast agents include, for example, suspensions of solid particles, emulsified liquid droplets, and gas-filled bubbles. See, e.g., Hilmann et al., U.S. Pat. No. 4,466,442, and published International Patent Applications WO 92/17212 and WO 92/21382.
Ultrasound has also been used in various therapeutic applications. One therapeutic use of ultrasound is known as hyperthermia. Hyperthermia involves insonating a targeted tissue mass, such as a tumor, with focused ultrasonic waves in order to heat the targeted mass. Application of heat to the tissue mass results in a retardation of growth of, or a shrinking of, the mass. The heating effects of therapeutic ultrasound can be enhanced by the introduction of microbubbles into the region under treatment, as described in D'Arrigo, U.S. Pat. No. 5,215,680.
Another therapeutic use of ultrasound, which is described in published International Patent Application WO 94/28873, involves administering a quantity of vesicles to a patient and monitoring the vesicles, for example using diagnostic ultrasound, until the presence of the vesicles is detected in a region of interest. Therapeutic ultrasonic waves are then applied to the region in order to rupture the vesicles for therapeutic purposes. For example, the vesicles may be combined with a bioactive agent that is released upon rupture of the vesicles, thus achieving targeted delivery of the bioactive agent in the region of interest.
Therapeutic ultrasound is typically carried out at different frequencies than diagnostic ultrasound. Specifically, it is desirable to perform therapeutic ultrasound at lower frequencies in order to achieve low attenuation, whereas higher frequencies are employed in diagnostic ultrasound to obtain better resolution.
There has been some effort in the prior art to provide systems that permit diagnostic ultrasound to be carried out simultaneously with therapeutic ultrasound, particularly therapeutic applications involving hyperthermia. Schaetzle, et al., U.S. Pat. No. 5,391,140, describe an apparatus having a diagnostic ultrasound capability that operates simultaneously with the application of therapeutic acoustic waves for localized hyperthermia. The system employs a transducer assembly that includes both diagnostic transducer elements and therapeutic transducer elements. The diagnostic transducer elements form a central array that is surrounded by the therapeutic transducer elements. Placing the therapeutic transducer elements outwardly of the centrally located diagnostic transducer elements enables the therapeutic acoustic waves to be more accurately focused in hyperthermia applications to achieve greater heating of biological tissues. However, the central location of the diagnostic transducer elements limits image quality and resolution.
Driller et al., U.S. Pat. No. 4,484,569, Coleman et al., U.S. Pat. No. 4,932,414 and Wurster et al., U.S. Pat. No. 5,005,579 all describe various systems that combine diagnostic ultrasound capabilities with therapeutic, hyperthermia capabilities, although not necessarily simultaneously.
The transducer assemblies and systems employed in these prior art systems are relatively complex and expensive to manufacture. Moreover, to the extent that these systems may be capable of performing diagnostic and therapeutic ultrasound simultaneously, their therapeutic ultrasound capabilities are designed primarily for, and therefore limited to, use in hyperthermia applications. None of these systems are suitable for carrying out ultrasonic imaging simultaneously with the ultrasonic rupture of vesicles for purposes such as enhanced cavitation or the targeted delivery of a bioactive agent to a region of a patient. Accordingly, methods and apparatus for providing such a capability are needed. The present invention satisfies this need.